1. Field of the Invention
The present invention generally relates to apparatuses for fusing an image onto a recording medium by heating and pressing the recording medium, and image forming apparatuses having such a fusing apparatus.
2. Description of the Related Art
Image forming apparatuses such as copy machines, printers, facsimile machines, and multifunction peripherals (MFP) are often equipped with a fusing unit configured to fuse a toner image that has been transferred on a recording medium onto the recording medium using heat and pressure. In one example, such a fusing unit includes a fusing roller in which a heating unit is installed, where an endless pressing belt is pressed onto the fusing roller using a pressing member.
When such a fusing apparatus is used to fuse a toner image onto the recording medium, such as a sheet of recording paper, the recording sheet with the toner image transferred thereon is passed through an area referred to as “a fusing nip” that is formed between the fusing roller and the pressing belt. The recording sheet is heated and pressed in the fusing nip so that the toner carried on the recording sheet can be heated and melted and thereby fused onto the recording sheet.
One of the problems which may be encountered during such a fusing operation is that the recording sheet may become attached to the surface of the fusing roller due to the adhesion of the molten toner, thereby preventing proper ejection of the recording sheet. Even if the recording sheet does not become attached to the fusing roller, it may become wound around the fusing roller as the sheet is transported, whereby the recording sheet is curled, which adversely affects the process of transporting or eventually stacking the recording sheets.
In order to overcome such problems, Japanese Laid-Open Patent Application No. 7-140831 discloses a fusing apparatus having a separating nail that contacts the fusing roller downstream of the fusing nip in a direction of transport of the recording sheet. The separating nail is configured to separate the recording sheet from the fusing roller so that the recording sheet does not become wound around the fusing roller.
Japanese Laid-Open Patent Application No. 2007-310210 discloses a fusing apparatus in which a separating roller smaller in diameter than the fusing roller contacts the fusing roller downstream of the fusing nip in the recording sheet transport direction. It is discussed in this publication that the recording sheet can be separated from the fusing roller as the recording sheet is transported along the separating roller.
However, installation of such separating units as the separating nail or the separating roller for ensuring proper separation of the recording sheet increases the size and cost of the fusing apparatus.